Single pass medical electrical lead

ABSTRACT

The present invention is directed to a single pass medical electrical lead. In one embodiment, the lead features a pair of bipolar electrodes positioned along the lead body so that they are positioned in the ventricle and atrium respectively when the lead is implanted. The lead body features a 90 degree bent reinforced section. The bend has a radius of curvature approximately 13 mm and begins approximately 90 mm from the distal end. This curved section is approximately 40 mm in length when straightened. The ventricular electrodes are positioned approximately 28 mm apart. The ventricular cathode electrode is positioned at the distal end of the lead. The atrial electrodes are positioned approximately between 5-35 mm apart, with 28 mm preferred. The atrial anode is located at a position immediately adjacent and proximal the 90 degree bent reinforced section.

FIELD OF THE INVENTION

This invention relates to the field of body-implantable medical devicesystems, and in particular to a body-implantable medical device systemwhich includes a single pass medical electrical lead.

BACKGROUND OF THE INVENTION

Modern electrical therapeutic and diagnostic devices for the heart, suchas pacemakers, cardioverters and defibrillators for example, require areliable electrical connection between the device and a preselectedregion of the heart. Typically an electrical "lead" is used for thedesired electrical connection.

One type of commonly used implantable lead is an endocardial lead.Endocardial leads are attached at their proximal end to an implantablepulse generator and at their distal end to the endocardium of a cardiacchamber. Such leads normally take the form of a long, generallystraight, flexible, insulated conductor having one end electricallyconnected to the pulse generator and the other end electricallyconnected to the endocardium through an electrode. Among the manyadvantages of an endocardial lead is that it may be positioned into theheart by sliding the lead through a vein until the electrode is properlypositioned, rather than physically exposing the heart itself.

The specific design of the endocardial lead used has often varieddepending upon the region of the heart to which it is to be connected,in particular whether it is for a ventricular application or an atrialapplication.

Ventricular endocardial leads are often readily flexible and have tinesor fins at their distal end. These tines are provided to engage thetrabeculation within the ventricle so as to reliably fix, or at leastposition, the electrode in the desired location. Unlike the ventricles,the atrial walls are relatively smooth. Because the atrial walls aresmooth it has been difficult to retain the electrode in a fixed positionwith respect to the wall of the atrium. One approach commonly used hasbeen to form the distal end of an atrial lead in a J-shapedconfiguration. Such a configuration causes the distal end to curveupwardly once the lead is within the atrium so as to provide reliablecontact between the electrode and the heart tissue.

In dual chamber pacing, however, it is necessary to establish anelectrical connection with both chambers of the heart. Typically thisnow involves the placement of two leads, a ventricular lead as well asan atrial lead, within the patient's heart. Usually the ventricular leadis placed first, i.e. it is passed through a blood vessel and into theventricular cavity. When the ventricular pacing lead has been stabilizedwithin the heart, the second lead, or atrial lead, is passed through theblood vessel and is moved into a selected position within the atrialcavity.

The placement of two separate pacing leads into two separate chambers ofthe heart, however, is a relatively complicated procedure. First as thesecond lead is being inserted, it is possible to strike the first leadwith the second lead thereby dislodging the first lead from its desiredposition. In addition, the presence of two leads may cause a significantdecrease in blood flow through the blood vessel, especially in patientshaving relatively small diameter vessels. Finally, although transvenousplacement of a lead is relatively not traumatic, it would nonetheless bebeneficial to simplify and shorten the implant procedure as much aspossible. Reducing the number of leads implanted from two to one wouldbe of significant benefit.

Because of the difficulties encountered by placing two leads there hasbeen a considerable number of past attempts to design a single leadwhich provides an electrical connection to both chambers of the heart,often referred to as a "single pass lead." An early attempt at a singlepass lead was taught by Bures in U.S. Pat. No. 3,865,118. Because theconfiguration taught by Bures requires the ventricular lead to becoaxially mounted within the outer sheath, minimal control could beexercised over placement of the atrial electrodes. To compensate forthis lack of control, Bures taught the use of opposing (i.e., spaced by180 degrees) spring loaded electrodes. Such a placement technique issusceptible to dislodgement, however. It is also electricallyinefficient because of the relatively large surface area of theelectrode and the difficulty in controlling the amount of that surfacearea actually in contact with the atrial wall. Furthermore, using theouter catheter to control flexure of the atrial electrodes lead tosealing problems.

Lajos in U.S. Pat. No. 4,057,067 attempted to solve many of the controlproblems found with the lead taught by Bures by using a "J" shapedatrial lead with stylet control. Because the atrial and ventricularleads, however, were spaced a fixed distance, the lead taught by Lajosdid not accommodate various sized hearts. A further problem with theLajos lead was the establishment of an effective seal of the hole at thedistal end of the atrial electrode. During insertion, this hole isblocked by the styler. Removal of the stylet, however, permitted seepageof blood into the lead.

A third single pass lead configuration was taught by Sabel in U.S. Pat.No. 3,949,757. Sabel used the "J" shaped atrial electrode placement astaught by Lajos but slid the atrial catheter within the outer sheath ofthe ventricular catheter. This solved one problem of Lajos by notrequiring an aperture in the distal end of the atrial electrode forstylet straightening of the "J" shape. It did not completely solve theproblem of differing heart sizes, however. The distance between thedistal end of the atrial catheter and the distal end of the outer sheathwas essentially fixed by practical factors even though the atrialcatheter was slidably mounted within outer sheath because sliding of theatrial catheter also changed the shape of the "J". The atrial electrodemay be lowered in the atrium by moving the atrial catheter eitherproximal or distal relative to the outer sheath. However, the atrialelectrode may not be raised within the atrium. That distance iseffectively established by the prior implantation of the ventricularelectrode. Providing a larger distance between the ventricular electrodeand the distal end of outer sheath would tend to distort the "J" shapeof the atrial catheter.

Another proposed configuration for a single pass lead was disclosed byGold in U.S. Pat. No. 4,444,195 which disclosed a flexible catheterhaving a series of ring electrodes selectively utilized for pacing andsensing in both chambers of the heart. As discussed above, onesignificant problem with this configuration was the reliable, consistentand acceptable placement of the atrial electrodes.

A still further attempt to configure a single pass lead was disclosed byHarris in U.S. Pat. No. 4,627,439 which featured a single pass leadhaving a prebent atrial section. In particular the atrial section had abend with the electrodes positioned on the bend. The bend, it was taughtwould assist in properly maintaining the position of the atrialelectrodes. The Harris design, however, failed to provide an acceptablesingle pass lead. In particular the configuration of the prebent sectionhaving electrodes on the bend failed to provide acceptable chronicelectrode position.

SUMMARY OF THE INVENTION

The present invention is directed to a single pass medical electricallead. In one embodiment, the lead features a pair of bipolar electrodespositioned along the lead body so they are positioned in the ventricleand atrium respectively when the lead is implanted. The lead bodyfeatures a reinforced section preferably having a 90 degree bend. Thebend has a radius of curvature approximately 13 mm and beginsapproximately 90 mm from the distal end. This curved section isapproximately 40 mm in length when straightened. The ventricularelectrodes are positioned approximately 28 mm apart. The ventricularcathode electrode is positioned at the distal end of the lead. Theatrial electrodes are positioned approximately between 5-35 mm apart,with 28 mm preferred. The atrial anode is located at a positionimmediately adjacent and proximal the 90 degree bent reinforced section.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-described and other aspects of the present invention may bebetter understood and appreciated with reference to a detaileddescription of a specific embodiment of the invention, when read inconjunction with the accompanying drawings, wherein:

FIG. 1 is a perspective view of the lead implanted in a heart;

FIG. 2 is a plan view of the lead;

FIGS. 3a and 3b are detailed sectional views of a proximal section ofthe lead body;

FIG. 4 is a detailed view of the reinforced section of the lead;

FIG. 5 is a detailed sectional view of the atrial electrode assemblypositioned on the reinforced section of the lead;

FIGS. 6 and 7 are detailed sectional views of the reinforced section;

FIGS. 8 and 9A-D depict alternate embodiments of the atrial electrodeassembly positioned along the reinforced section of the lead;

FIG. 10 is a sectional view of the distal section of the lead;

FIGS. 11 and 12 depict the repositioning of the atrial electrodeassembly within an atrium of the heart by rotating a proximal end of thelead;

FIG. 13 is a detailed side view of the reinforced section of the leadshowing the bend caused by a torque to the proximal end of the lead; and

FIG. 14 is a detailed bottom view of the reinforced section of the leaddepicted in FIG. 13.

It should be understood the drawings are not necessarily to scale.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is described within the context of a single passbipolar transvenous endocardial lead adapted for use in connection withan implantable cardiac pulse generator, such as the "™" or "™" as wellas other models commercially available from Medtronic, Inc.,Minneapolis, Minn. The present invention, however, may be advantageouslypracticed in conjunction with many different types of implantablemedical devices as well as many other various embodiments of therapeuticor diagnostic catheters and is not limited only to medical electricalleads. For purposes of illustration only, however, the present inventionis below described in the context of a transvenous endocardial lead.

The Lead

FIG. 1 is a perspective view of a lead according to the presentinvention implanted within a heart. As seen lead 1 consists essentiallyof a lead body 2 and a connector assembly 3. Lead body 2, in turn, hasessentially three sections: a distal section 4, a reinforced section 5and a proximal section 10. As seen reinforced section 5 has a larger orheavier insulative cover so as to be less flexible or more stiff thaneither of the other sections and furthermore to have a permanent bend(as best seen in FIG. 2, discussed in detail below.) In a preferredembodiment the permanent bend of reinforced section 5 is between 135 and45 degrees, where 90 degrees is preferred.

In an alternate embodiment reinforced section 5 has a permanent bendbetween 135 and 45 degrees along a first plane, between 5 and 90 degreesin a second plane and between 5 and 90 degrees in a third plane. Otherdegrees of bend the planes may further be used and be within the scopeof the present invention.

The flexibility and bend relationship among these sections is importantin the present invention because it maintains the atrial electrodes 20,21 in their desired position. In particular reinforced section 5essentially functions as a spring to thereby cause the atrial electrodes20, 21 to contact or be disposed very near atrial wall 22 and therebyprovide a suitable electrical connection with the atrial tissue.Reinforced section 5, moreover, is flexible so as to permit the leadbody and thus atrial electrode assembly 18 to conform along with theheart as it contracts and, in addition, to be positioned in a specificarea of the atrial tissue by adjusting lead 1 at its distal end.

Lead 1 is constructed as follows: A connector pin assembly 3 ispositioned at the proximal end of lead body 2, as best seen in FIG. 2.Connector pin assembly 3 features a pair of connector pins 30, 31electrically connected to lead body 2 by bifurcation 32. Connector pinassembly 3 provides an electrical coupling between lead 1 and animplantable pulse generator (not shown.) Each connector pin 30, 31 hassealing rings 33 and terminal pin 34, all of a type known in the art. Ina preferred embodiment each connector pin 30, 31 is constructed to meetthe industry standard IS-1 Bi. Furthermore, while in the preferredembodiment a pair of connector pins are provided, a single quadrapolarconnector pin may alternatively be used, as is known in the art.

An anchoring sleeve 35 may also be provided for suturing lead body 2 tobody tissue. Anchoring sleeve 35 and connector pin assembly 30, 31 arepreferably fabricated from silicone rubber, although they may also beconstructed of any other suitable biocompatible material known in theart.

One connector pin 30 may also include stylet guide 40 and styletassembly 41 coupled to terminal pin 34 for imparting stiffness to lead 1during placement, as discussed in detail below. Stylet guide 40 andstylet assembly 41 are typically discarded after use and beforeconnection of lead 1 to a pacemaker pulse generator (not shown.)

Proximal section 10 of lead body 2 extends from bifurcation 32 toreinforced section 5 and has a length of between 302 mm and 327 mm,where 315 mm is the preferred length.

As best seen in FIGS. 3a and 3b, which show a sectional and fragmentedviews of proximal section 10 of lead body 2, lead body 2 consists of aquadralumen sleeve 42 having four conductors 43, 44, 45 and 46(conductor 46 is obstructed by conductor 45 in this particular view)positioned within the respective lumens 47, 48, 49 and 50. Sleeve 42 ispreferably constructed from silicone and may be surface treated on itsouter surface or its inner surface or both according to the teachings ofU.S. Pat. No. 5,133,422 entitled "Radio Frequency Glow Discharge SurfaceTreatment of Silicone Tubing Used as a Covering For Electrical Leads toImprove Slip Properties Thereof" and U.S. patent application Ser. No.08/239,007 entitled "Plasma Process for Reducing Friction Within theLumen of Polymeric Tubing" both of which are incorporated herein byreference. Conductors 43-46 are multifilar coils and preferably areconstructed from MP35N.

Turning now to the details of reinforced section, FIG. 4 showsreinforced section 5 in whole while FIG. 5 shows a cross-sectionalfragmented view of the region of reinforced section 5 where atrialelectrode assembly 18 is positioned. As previously discussed above,reinforced section 5 is preferably less flexible than either proximalsection 10 or distal section 4 due, in part, to the larger or heavierinsulative material used. In the preferred embodiment this material issilicone.

As best seen in FIG. 4 reinforced section has essentially threeportions: curved portion 23 having a straight leg portion at either end,viz. proximal straight leg portion 24 and distal straight leg portion25. Curved portion 23 preferably has a radius of curvature of between12.5 mm-13.5 mm, with 13 mm preferred, proximal straight leg portion 24has a length of 38.5 mm-39.5 mm, with 39 mm preferred and distalstraight leg portion 25 has a length of between 9.5 mm-10.5 mm with 10mm preferred. As seen, proximal straight leg section 24 features atrialelectrode assembly 18. Atrial electrode assembly 18, in turn, comprisesa first electrode 20 and second electrode 21.

In the preferred embodiment first electrode 20 of atrial electrodeassembly 18 functions as the cathode and is a whole ring having asurface area of 15 sq. mm. Preferably the ring is constructed of aplatinum ring and coated over its external surface with a plating ofplatinum black as is well known in the art. First electrode 20 furtherpreferably features a helical ridge, as best seen in FIG. 4, to providebetter electrical properties, as is well known in the art. See, forexample, the U.S. Pat. No. 4,502,492 of Bornzin. Second electrode 21preferably functions as the anode and is a whole ring of a polishedplatinum iridium alloy having a surface area of 36 sq mm. In thepreferred embodiment first electrode 20 is positioned at the proximalend of proximal straight leg 24 of reinforced section 5. Secondelectrode 21 is distally positioned from first electrode 20 alongproximal straight leg 24 at a distance from first electrode 20 ofbetween 5-35 mm, with 28 mm preferred.

FIGS. 6 and 7 provide additional details of the construction ofreinforced section 5 and in particular the joining of reinforced section5 and distal section 4. As best seen in FIG. 7 reinforced section 5, andin particular curved portion 23 and distal straight leg portion 25 has apair of lumens therethrough in which conductors 45 and 46 run. Conductor46 has dog leg 51 so that conductors transition from a side by sidearrangement to a coaxial arrangement. As seen distal section 4 hasconductors 45, 46 arranged coaxially. An additional embodiment of theatrial electrode assembly 18 may be seen in FIG. 8, in which atrialelectrodes 20, 21 are half rings rather than whole rings.

A still further alternate embodiment of atrial electrode assembly 18 ofthe present invention may be seen in FIG. 9A which discloses providingtines 64 about atrial electrode assembly 18 to permit fixation to atrialtissue.

In addition, while the atrial electrode assembly 18 is preferablypositioned strictly along straight portion 24 of reinforced section 5,it may additionally be positioned so as to be only partially alongreinforced section 5, such as being positioned somewhat more proximalsuch that first electrode 20 is positioned along proximal section 10 oflead body 2, as seen in FIG. 9B. Likewise atrial electrode assembly 18may further be positioned so as to be only partially positioned alongproximal straight leg portion 24 such that second electrode 21 ispositioned along curved portion 23, as seen in FIG. 9C, or positionedalong distal straight leg portion 25, as seen in FIG. 9D. Other variousconfigurations and placements of atrial electrode assembly 18 along leadbody 2, and in particular with reference to curved portion 23, andproximal straight leg portion 24 and distal straight leg portion 24 ofreinforced section 5 may be used and still be within the scope of thepresent invention. Moreover, as seen, tines 64 may be either slanted inthe proximal direction or in the distal direction or both.

Distal section 4 of lead body is connected at the distal end ofreinforced section 5 and in particular to the distal end of bent portion23. Distal section 4 has ventricular electrode assembly 70 mountedthereto and preferably is constructed as is the distal end of theMedtronic Lead Model No. 5024M. As seen in FIG. 10 distal section 4consists generally of fixation assembly 71 and ventricular electrodeassembly 70. Electrode assembly 70 is, in the disclosed embodiment, ofthe bipolar type and has tip electrode 72 at its distal end and a ringelectrode 73 spaced proximally back from the distal end between 26.7mm-29.3 mm, with 28 mm preferred. As will be appreciated by those ofordinary skill in the art, tip electrode 72 and ring electrode 73 arecoupled to separate, insulated lead conductors.

As best seen in FIG. 7 distal section 4 of lead body 2 has concentriclumens through which the conductors 45, 46 run to tip electrode 72 andring electrode 73 respectively. As noted earlier conductors 45, 46 arepreferably multi filar coils of MP35N or any other suitable alloy suchas a platinum-iridium alloy. As seen in FIG. 10, lead body 2 has anouter flexible insulative sheath 74 made from silicone rubber whichjoins into reinforced section 5 by medical adhesive 88. Outer insulativesheath 74 covers conductor 46. Conductor 46 extends along through leadbody 2 and terminates at its distal end where it is electricallycoupled, for example by spot or laser welding, to a crimp sleeve 75 madeof stainless steel or the like. Crimp sleeve 75, in turn, is inelectrical connection with a sleeve 76 which is similarly made ofstainless steel or the like. Sleeve 76 is engaged within and inelectrical contact with substantially cylindrical ring electrode 73,which is preferably made of a 90/10 platinum/iridium alloy and has asurface area of 36 sq mm.

Partially engaged between ring electrode 73 and tip electrode 72 is atip/ring spacer 77 made of silicone rubber. Positioned near the distalend of tip/ring spacer 77 are a series of tines 80 as are well know inthe art. Conductor 45 is electrically connected to electrode 72 throughcrimp cylinder 81 and crimp core 82. Thus lumen 47 of conductor 45extends the length of lead 1, from connector pin 30 to tip electrode 72.As seen electrode 72 has a hole 83 therethrough communicating withhollow 84. Located within hollow 84 is a monolithic controlled releasedevice (MCRD) 85 to dispense a drug, preferably with ananti-inflammatory agent, e.g. a steroid dexamethasone sodium phosphate.

Tip electrode 72 is preferably a porous platinum compositionelectroplated with platinum black. The porosity, together with theplatinum black coating is intended to reduce source impedance andpolarization. The porous structure may be made by mixing a conductivematerial and a binder to form a slurry mixture. The slurry mixture mayconsist of 70 weight percent of a spherical platinum powder and 30weight percent of a binder solution. The preferred binder solutionconsists of 2 percent of an organic binder, such as "KLUCEL™"manufactured by Aqualon Corp. of Wilmington, Del. and 98 percentdeionized water. This slurry is formed into the desired shape andsintered. Once sintered the porous structure is then preferablyelectroplated with a material to provide a relatively high microscopicsurface area, such as platinum black in the preferred embodiment.Electroplating may be accomplished in any manner suitable so as todeposit a layer of platinum black is deposited over the entire area ofthe electrode. This produces an electrode having a platinum blacksurface coating which is sufficiently durable to permit it to beimplanted within the body. The porosity, together with the platinumblack coating is intended to reduce source impedance and polarization,as is well known in the art.

The steroid also is deposited within the pores of tip electrode 72 as iswell known in the art. In a preferred embodiment electrode 72 has amacroscopic surface area of less than 5.8 sq mm. The surface ofelectrode 72 exposed to the body tissue or fluids or both is generallyhemispherical. The small geometric macroscopic electrode size isintended to produce very high pacing impedance. The porous surfaceconfiguration together with platinum black electroplating and steroidcontribute to a microscopically large surface area for low polarization,low source impedance and low thresholds. The porous surface alsofacilitates the retention of steroid and adhesion of the platinum blackto the electrode surface.

Method of Implanting the Lead

Transvenous implantation of lead 1 may be accomplished as follows:

First, lead 1 has styler assembly 41 inserted through lumen 47 ofconductor 45 so the distal end of stylet assembly 41 is adjacent thedistal end of lead 1. Stylet assembly 41 is used to impart stiffness tolead 1 and provide steerability, in addition and more importantly,stylet assembly 41 causes lead 1 to straighten bend of reinforcedsection 5 so lead 1 may be introduced through the venous system. Asdepicted in FIG. 2 a stylet guide 40 may be temporarily mated overterminal pin 34 of terminal assembly 30 to facilitate the introductionof stylet assembly 41.

Next lead 1 may be introduced into the venous system in any of the waysknow in the art, such as through a sub clavian approach. Lead 1 is thenpushed through the venous system until tip electrode 72 is positionedwithin atrium 19.

Stylet assembly is then withdrawn partially from lumen, preferablyapproximately 10 cm, and lead 1 is continued to be pushed through venoussystem until tip electrode 72 is positioned proximate ventricular apex17 and styler assembly 41 is then withdraw from lumen.

As seen in FIGS. 1, 11 and 12 the unique design of lead 1, and inparticular due to the construction, including the relative stiffness,dimensions and shapes of the proximal section 10, reinforced section 5and distal section 4, once styler is removed, lead 1 takes a shape suchthat tip electrode remains positioned at apex 17 while atrial electrodeassembly 18 contacts atrial wall 22. Reinforced section 5, although lessflexible than proximal section 10 and distal section 4 (distal section4, in turn is less flexible than proximal section 10) causes atrialelectrode assembly to remain in direct contact or extreme closeproximity to atrial wall 22. In such a manner atrial tissue may bereliably sensed as well as stimulated through atrial electrode assembly18.

An additional important feature is depicted in FIGS. 11-14. As seen,rotation of a proximal end of lead 1 in direction 90 causes atrialelectrode assembly to move in a path as shown. That is, rotation atproximal end causes atrial electrode assembly 18 to move against or"swipe along" atrial wall 22. This movement permits atrial electrode 18to be optimally positioned along the atrial tissue, and in addition, tocontinuously maintain an electrical connection therewith. Besidesrotation of the distal end of lead 1, atrial electrode assembly 18position may also be influenced by the relative amount of lead bodyinserted into the venous system, that is the amount of lead body distalto the anchor sleeve 35. Thus it is believed a particularly usefulanchor sleeve 35 design would be that shown in the U.S. Pat. No.5,273,053 issued to Pohndorf and entitled "Suture Sleeve with LeadLocking Device."

An important feature of the lead 1, besides allowing the adjustment ofthe position of the atrial electrode assembly 18 by rotation of proximalend of lead 1 as well as the amount of lead body distal to anchor sleeve35, is that while this adjustment is occurring the ventricular electrodeassembly is not moved and maintains capture. This is due to the relativestiffness and shape of the reinforced section 5 and the position of theatrial electrode assembly 18 thereon.

Although a specific embodiment of the invention has been disclosed, thisis done for the purposes of illustration and is not intended to belimiting with regard to the scope of the invention. It is contemplatedthat various substitutions, alterations, and/or modifications, includingbut not limited to those specifically discussed herein, may be made tothe disclosed embodiment of the invention without departing from thespirit and scope of the invention as defined in the appended claims,which follow.

What is claimed is:
 1. A body-implantable medical electrical leadcomprising:a lead body having a straight distal section, an intermediatesection and a straight proximal section, said proximal section moreflexible than said distal section, said distal section being moreflexible than said intermediate section, the lead body having a firstconductor and a second conductor section; a first electrode positionedon said proximal section and coupled to the first conductor, and asecond electrode positioned on said distal section and coupled to thesecond conductor.
 2. The medical electrical lead according to claim 1wherein said intermediate section has a bend.
 3. The medical electricallead according to claim 2 wherein said bend is between 135 and 45degrees.
 4. The medical electrical lead according to claim 3 whereinsaid bend is 90 degrees.
 5. The medical electrical lead according toclaim 2 wherein said intermediate section further having a proximalstraight leg portion attached to a proximal end of said bend and adistal straight leg portion attached to a distal end of said bend. 6.The medical electrical lead according to claim 5 wherein a thirdelectrode is positioned on said proximal straight leg section of saidbend.
 7. The medical electrical lead according to claim 1 wherein saidfirst electrode has a porous platinized surface.
 8. A lead in accordancewith claim 1 wherein the first electrode has a monolithic controlledrelease device.
 9. An electrode assembly in accordance with claim 8wherein the first said electrode has a drug-elution port.